Conventionally, with an object to prevent forgery, magnetic ink including magnetic material has been used for printing on paper sheets such as checks, merchandise coupons, etc. Security techniques have been advancing year after year, and in recent years, there have been proposed paper sheets in which one paper sheet includes plural types of magnetic materials with different magnetic properties. For such paper sheets, it is necessary to determine each magnetic material included in the paper sheet to determine the authenticity of the paper sheet.
An example of an apparatus that determines plural types of magnetic materials included in a paper sheet has been disclosed in Patent Document 1. This document discloses an apparatus that determines magnetic materials with mutually different coercive forces. In this apparatus, a high-coercive force magnetic material and a low-coercive force magnetic material are magnetized in the same magnetization direction by a first magnet with a high magnetic force, and a detection signal corresponding to the magnetism of both the magnetic materials is obtained by using a first sensor. Subsequently, the magnetization direction of the low-coercive force magnetic material is changed by using a second magnet with a low magnetic force, and then a detection signal corresponding to the magnetism of the high-coercive force magnetic material only is obtained by using a second sensor. A difference between the detection signal obtained by the first sensor from both the high-coercive force magnetic material and the low-coercive force magnetic material and the detection signal obtained by the second sensor from only the high-coercive force magnetic material is taken as a detection signal obtained from only the low-coercive force magnetic material.